The invention relates to a method for treating tobacco with volatilizable flavorants. In particular, it relates to a method for uniformly depositing menthol vapor on tobacco.
In the past the application of flavorants, including menthol, to tobacco has often been a rather haphazard operation. In general, menthol has been applied to tobacco by first forming a dilute menthol solution and thereafter spraying the solution onto tobacco. It is well known that during spraying operations, tobacco is contacted only by discrete spray droplets of menthol solution. Such droplets are not uniformly distributed over the surface of the tobacco with the result that conventional spraying operations do not, for the most part, provide uniform deposition of menthol. Only through subsequent blending and menthol transferring operations can uniform deposition be obtained.
In an attempt to remedy the aforesaid deficiencies it has been proposed to feed tobacco into a conduit where it is mixed with an air stream. The tobacco-air mixture is combined with an alcohol-menthol mixture which is sprayed onto the tobacco. This method, disclosed in U.S. Pat. No. 3,548,838, has various defects. The patent teaches that a menthol solution must be formed, preferably employing an alcohol solvent. The use of alcohol as a solvent for menthol is expensive and hazardous. As illustrated in the patent, it is necessary to vent the tobacco mentholating system to prevent the formation of an explosive concentration of alcohol vapors. The venting procedure permits a substantial loss of menthol from the system. Further, it may be necessary to permit the tobacco to stand after contact with the menthol-alcohol solution for at least 4 hours prior to use.
An additional defect of the above patent and indeed, of the prior art menthol spraying procedures, lies in the failure to control the level of menthol application during a continuous processing operation. In any direct contact spray system it is necessary to maintain matched flows of both tobacco and menthol solution. When any variations occur in either flow, off target levels for menthol application occur. No convenient method has been proposed to immediately monitoring the application of menthol on tobacco and of rapidly compensating for any variation therein. This is basically an inherent defect in the prior art processes, since spray droplets require time to spread over the surface of the tobacco. There is no convenient way of rapidly monitoring and adjusting for variations in levels of menthol application and other flavorants via the spray process.
The tobacco industry has long desired to apply menthol vapor directly to tobacco in a continuous application process. However, the industry has not been able to overcome the problems associated with such a process. In fact, U.S. Pat. No. 3,548,838 warns that it is impractical to mix menthol directly with tobacco since it is too difficult to control the very minor quantities which it is desired to use. The patent further teaches that adsorption of menthol on cut blend tobacco in a closed air recirculation system is not feasible, since, in order to provide an acceptable contentration of menthol vapor in the system, it has allegedly proven necessary to operate at extremely high temperatures, well in excess of 200.degree. F. Such high temperatures are not conducive to tobacco processing.
Accordingly, there exists a long felt need for a process for uniformly applying menthol and other flavorants directly to tobacco without employing sprayed, dilute solutions, free of the side effects and deficiencies of the prior art.